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Another main lug question

Posted by sclub (My Page) on
Wed, Mar 19, 14 at 23:01

Hi all,
I have read through a number of posts that deal with wiring main lugs and sub panels, etc., but don't feel like any of these help out in my situation.

My wife and I have bought a house with aluminum wiring (pig tailed however), and I have decided to rewire it w/ copper. While I'm at it, I have decided to change the existing breaker panel as it's out of space and quite old.

The setup in the house is that there is a main breaker (a single breaker on the outside and 2x 100A fuses on the inside) that feeds the main lug (my main panel). I'll refer to them as the 'main breaker' and 'main lug' from now on in this post.

My understanding is that when wiring a sub-panel, which technically my main lug is; one needs to have 4 wires (2 hot, a neutral and a ground). Looking at the existing connectivity, I only see two hot, and a neutral connected to the neutral bar in the main lug. Now keep in mind that there are wires everywhere in the main lug so I might be missing something here.

My first question is:
1. Is it possible to have only three wires connecting main lug and main breaker, and still have everything come up clear when checking plugs for correct wiring with the receptacle tester?

My other question deals with the main panel I bought in order to replace my main lug. I purchased a Siemens XP32100 (only picture I could find is located here: This panel seems to be specific to Canada as I haven't seen it on any of the US sites.

In order to prep the panel to act like a sub panel that it is, I have disconnected the bar at the bottom (it connects ground bar and the neutral bar). This has resulted in the following:
1. The long bar on the left is not moving as it is still connected to the case via screwed copper strip
2. The long bar on the right is moving up and down as it sits on something that looks like a plastic channel. I will contact Siemens to find out how to stop it from moving tomorrow.

I have two questions here:
1. I am assuming that two small bars that can be seen in the picture can be used as grounding bars
2. Am I supposed to remove the screw connecting the long bar on the left from the case even if I intend to use it as a grounding bar?

Your help on the above matters is greatly appreciated.

Thank you,


Follow-Up Postings:

RE: Another main lug question

The thing called the "main breaker" is properly called the service disconnect. This is the only place where NEUTRAL and GROUND should be connected. Your "Main Lug" is a sub panel as you realize.

I'm not particularly fond of the Siemens panels. Perhaps the new ones are OK, but these are a derivation of an older piece of unreliable junk that I ripped out of my house.

The bar at the bottom connecting the two bars comes out in your application. The bar rigidly connected to the case is the ground bar and the one sitting on the plastic standoffs is then the neutral bar.

RE: Another main lug question

Hi ronnatalie,
Thank you very much for your reply, and thank you for providing correct terminology (this should make it easier to communicate). This time around I have included an amazingly life like sketch of my panel that should also help out with the communication.

Following your response I have a couple of questions:
1) Now that I have disconnected the two long strips from each other (let's call them ground bar and the neutral bar), do I need to unscrew the ground bar from the service panel case (as you can see from the picture it is connected with a screw). I guess my question is, should any of the bars in the service panel (main lug/sub panel) be connected to the case of said panel?

2) The two short strips on the side of the longer bars, are they pre-installed ground strips/bars?

3) The cable connecting the service disconnect and the main lug is currently (AFAI tell) comprised of only three wires (2 hot + neutral). Do i need to have a fourth wire for ground between the service disconnect and the main lug?

4) I went with Siemens because it had a package in the orange store that included a large number of breakers, most notably single pole 20A that would fit nice in my kitchen. I was disappointed that all the breakers provided were 'full size' and not 'space savers' (I think these might be called tandem, but correct me if I'm wrong). Do you think that returning the set and going with Square D would be a better choice and just buying 'tandem' breakers separately (didn't notice any company's bundle offering 'tandem' breakers in their set) to save on the space inside the panel?

Thank you for taking time to look and (hopefully) answer these questions.

RE: Another main lug question

You have a problem, now you have a neutral bus and a grounding bus but no grounding conductor to connect to the grounding bus. Unless the sub panel is fed with metal conduit this configuration is more dangerous than if you had left it alone. It is also illegal to install a sub panel with only 3 conductors, unless it is 120 volts only or has a metallic path back to the service entrance to carry fault current.
If you indeed have no grounding path you must install a new feed to your sub panel.

This post was edited by joefixit2 on Thu, Mar 20, 14 at 21:03

RE: Another main lug question

Hi joefixit2,
Thank you very much for taking time to contribute to my question. You have answered something that has been bugging me. Currently there is no danger of anything as this panel is not installed yet; I am just trying to get some answers about it and I think you have provided it.

My existing main lug panel had no obvious ground wire going between it and the service disconnect that was necessary based on every book I read and video I watched on sub-panels. It also didn't have any wire going outside the panel providing grounding (which would be against the code, but still better than nothing).

This has been bugging me as when I would check the outlets with the receptacle tester everything would show up as proper. Your comment about the metallic conduit connecting the service disconnect and main lug answered my question. My existing main lug IS connected via metal conduit to the service disconnect, so that must be what is providing ground connectivity to the main lug (via service disconnect).

It would seem to me then that ground in the main lug needs to be connected to the metal casing of the panel, and that it needs to have some type of a connection between the grounds in the main lug and the service disconnect; either through a properly sized wire (for 100A, #6 is code for neutral in Ontario, so I'm assuming it's appropriate for the ground as well???) or through a metal conduit connecting the two panels.

Thank you joefixit2!

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